Global environmental and economic concerns regarding increasing fuel consumption and greenhouse gas emission, the rising cost of energy worldwide, and demands for lower operating cost, are driving changes to legislative regulations and consumer demand. As these regulations and requirements become more stringent, advanced engine technologies must be developed and implemented to realize desired benefits.
FIG. 1B illustrates several valve train arrangements in use today. In both Type I (21) and Type II (22), arrangements, a cam shaft with one or more valve actuating lobes 30 is located above an engine valve 29 (overhead cam). In a Type I (21) valvetrain, the overhead cam lobe 30 directly drives the valve through a hydraulic lash adjuster (HLA) 812. In a Type II (22) valve train, an overhead cam lobe 30 drives a rocker arm 25, and the first end of the rocker arm pivots over an HLA 812, while the second end actuates the valve 29.
In Type III (23), the first end of the rocker arm 28 rides on and is positioned above a cam lobe 30 while the second end of the rocker arm 28 actuates the valve 29. As the cam lobe 30 rotates, the rocker arm pivots about a fixed shaft 31. An HLA 812 can be implemented between the valve 29 tip and the rocker arm 28.
In Type V (24), the cam lobe 30 indirectly drives the first end of the rocker arm 26 with a push rod 27. An HLA 812 is shown implemented between the cam lobe 30 and the push rod 27. The second end of the rocker arm 26 actuates the valve 29. As the cam lobe 30 rotates, the rocker arm pivots about a fixed shaft 31.
As FIG. 1A also illustrates, industry projections for Type II (22) valve trains in automotive engines, shown as a percentage of the overall market, are predicted to be the most common configuration produced by 2019.
Technologies focused on Type II (22) valve trains, that improve the overall efficiency of the gasoline engine by reducing friction, pumping, and thermal losses are being introduced to make the best use of the fuel within the engine. Some of these variable valve actuation (VVA) technologies have been introduced and documented.
A VVA device may be a variable valve lift (VVL) system, a cylinder deactivation (CDA) system such as that described U.S. patent application Ser. No. 13/532,777, filed Jun. 25, 2012 “Single Lobe Deactivating Rocker Arm” hereby incorporated by reference in its entirety, or other valve actuation system. As noted, these mechanisms are developed to improve performance, fuel economy, and/or reduce emissions of the engine. Several types of the VVA rocker arm assemblies include an inner rocker arm within an outer rocker arm that are biased together with torsion springs. A latch, when in the latched position causes both the inner and outer rocker arms to move as a single unit. When unlatched, the rocker arms are allowed to move independent of each other.
Switching rocker arms allow for control of valve actuation by alternating between latched and unlatched states, usually involving the inner arm and outer arm, as described above. In some circumstances, these arms engage different cam lobes, such as low-lift lobes, high-lift lobes, and no-lift lobes. Mechanisms are required for switching rocker arm modes in a manner suited for operation of internal combustion engines.
One example of VVA technology used to alter operation and improve fuel economy in Type II gasoline engines is discrete variable valve lift (DVVL), also sometimes referred to as a DVVL switching rocker arm. DVVL works by limiting engine cylinder intake air flow with an engine valve that uses discrete valve lift states versus standard “part throttling”. A second example is cylinder deactivation (CDA). Fuel economy can be improved by using CDA at partial load conditions in order to operate select combustion cylinders at higher loads while turning off other cylinders.
The United States Environmental Protection Agency (EPA) showed a 4% improvement in fuel economy when using DVVL applied to various passenger car engines. An earlier report, sponsored by the United States Department of Energy lists the benefit of DVVL at 4.5% fuel economy improvement. Since automobiles spend most of their life at “part throttle” during normal cruising operation, a substantial fuel economy improvement can be realized when these throttling losses are minimized. For CDA, studies show a fuel economy gain, after considering the minor loss due to the deactivated cylinders, ranging between 2 and 14%.
Currently, there is a need VVA systems and devices that operate more efficiently, with additional capabilities over existing rocker arm designs.